1. Field To which the Invention Pertains
In the lower grades of grammar school, children are introduced to the concepts of weight and volume. Because these concepts are somewhat abstract, educators have realized the importance of providing children with an opportunity to relate these concepts to physical objects. Thus, it is desirable to provide children with weighing devices whereby they can conduct their own experiments to determine the weight of commonly encountered articles, as well as the relative weight of articles, for example the weight of a blackboard eraser versus the weight of one or more pieces of chalk. In the same context, it is also important for children to develop an understanding of the weight of liquids and granulated material, such as sand or salt.
To satisfy all these objectives, it is desirable to provide a child with a scale of the beam balance type whereby the weight of different articles may be compared to determine which is the heavier article. Also, with a scale of this type, a standard weight may be used to ascertain the actual weight of a particular article.
Although the desirability of providing children with a reasonably accurate and sensitive beam balance type scale is clear, the problems of designing and constructing such a scale are equally clear. For example, since the scale is to be used by children, it must be of a particularly rugged and simple construction. Additionally, in order to insure that schools can afford to purchase a number of these scales, the cost of the scale must be quite low. Although it may be a simple matter to provide a primitive beam balance type scale which is both inexpensive and sturdy, it must also be realized that such a scale should be reasonably accurate and sensitive. In the absence of reasonable accuracy and sensitivity, the entire educational objective will be frustrated. Thus, ideally it is desirable to provide a child with a beam balance scale which incorporates accuracy promoting features which are generally only found in expensive scales.
In summary, it will be seen that there are conflicting design criteria associated with providing an accurate, all purpose beam balance type scale for educational use by grammar school children. A scale of this type is the field to which this invention pertains.
2. Prior Art
A number of prior art patents disclose scales of the balance beam type, e.g. U.S. Pat. Nos. 423,183, 939,347, 1,351,449, 1,899,436, 2,272,142, 2,839,288 and 3,502,163.
In the area of beam balance scales for educational use by small children, perhaps the most relevant of these patents is U.S. Pat. No. 3,502,163. Although the construction of the beam balance scale disclosed in this patent appears to be sturdy and simple, the accuracy and sensitivity of this scale may be marginal in view of the fact that this scale does not include a so-called check lever. Scales which do not include a check lever may not produce an accurate weighing since, with such scales, a balance condition may or may not be obtained, depending upon the position of the weight on the weighing tray.